4,2

J. Goldman and G.-C. Rota, The number of subspaces of a vector space, pp. 75-83 of W. T. Tutte, editor, Recent Progress in Combinatorics. Academic Press, NY, 1969.

I. P. Goulden and D. M. Jackson, Combinatorial Enumeration. Wiley, NY, 1983, p, 99.

M. Sved, Gaussians and binomials, Ars. Combinatoria, 17A (1984), 325-351.

Sequence in context: A064252 A034625 A083598 this_sequence A035917 A115925 A029557

Adjacent sequences: A015297 A015298 A015299 this_sequence A015301 A015302 A015303

nonn,easy

Olivier Gerard (ogerard(AT)ext.jussieu.fr)